1. Field of the Invention
The present invention relates to an electrophotographic image-forming apparatus.
2. Description of the Related Art
A conventional electrophotographic image-forming apparatus performs a printing operation consisting of five electrophotographic processes: charging, exposing, developing, transferring, and fixing. A charging unit charges the surface of a photoconductor uniformly. An exposing unit in the form of an LED head or a laser head illuminates the charged surface of the photoconductor to form an electrostatic latent image. A developing unit applies triboelectrically charged toner to the electrostatic latent image by the Coulomb force, thereby developing the electrostatic latent image into a toner image. A transferring unit transfers the toner image onto a print medium that passes between the photoconductor and a transfer roller. Then, the print medium passes through a fixing unit where the toner image on the print medium is fused into a permanent image.
With the aforementioned conventional apparatus, oil is supplied to the surface of rollers of the fixing unit to prevent so-called xe2x80x9chot-offsetxe2x80x9d where the toner on the print medium is deposited on the rollers of the fixing unit. For an oil-free type fixing unit, toner contains a considerable amount of wax.
Especially for printing a color image on an OHP, the toner is required of heat fusibility having a very low viscosity. Therefore, oil needs to be supplied to the rollers of the fixing unit or wax needs to be added to the toner.
However, the wax contained in the toner is solid at room temperature. Wax is effective in preventing a problem of offset but has a disadvantage of a so-called xe2x80x9cfilmingxe2x80x9d where the wax deposited on toner-carrying members such as a developing roller and a developing blade serves as a paste to form a film of toner. The wax deposited on the toner-carrying members is an obstacle to forming uniform thickness of toner layer on the toner-carrying members. Further, toner deposited on the edge of the developing blade forms tiny projections that scratch the toner layer formed on the developing roller, preventing the toner from being deposited uniformly on the developing roller. xe2x80x9cFilmingxe2x80x9d causes deterioration of print quality.
An object of the present invention is to provide an image-forming apparatus capable of preventing xe2x80x9cfilmingxe2x80x9d where wax is deposited on toner-carrying members such as a developing roller and a developing blade serves as a paste to form a film of toner.
An image-forming apparatus includes a developing unit and a fixing unit. The developing unit includes a developing roller and a toner-supplying roller that supplies toner to the developing roller. The developing roller applies the toner to an electrostatic latent image on a photoconductor to form a toner image. The toner image is transferred onto a print medium, and finally fused into a permanent image. The toner includes a wax that remains solid at room temperature and melts at a fixing temperature. At least one of the toner-supplying roller and the developing roller is a silicone roller on which oligomer in the form of siloxane is deposited.
The silicone roller contains non-cured siloxane in the range of 10 to 8000 PPM.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.